1. Field of the Invention
The present invention relates to an ink-contacting thermoplastic elastomer composition for an ink jet printer, in particular, technology concerning the gas barrier characteristic, water vapor barrier characteristic, flex resistance, and tube moldability of an ink-contacting thermoplastic elastomer composition for an ink jet printer.
2. Description of the Related Art
An ink jet recording apparatus that performs recording on a recording medium by discharging ink from an ink jet recording head has been conventionally known. In the ink jet recording apparatus, the recording is performed by discharging the ink from the ink jet recording head while moving a carriage on which the ink jet recording head is mounted in the main scanning direction with respect to the recording medium. After one main scan, the recording medium is moved in a sub-scanning direction in a certain amount, and the carriage is moved in the main scanning direction again so that the recording may be performed. Repeating the operation enables the completion of the recording of a requested pattern on the recording medium.
The ink supply unit of the ink jet recording apparatus may be of such a type that an exchangeable tank filled with the ink (ink tank) is mounted separately from the carriage. Adopted in the ink jet recording apparatus of the type is a mechanism in which the ink tank and the ink jet recording head mounted on the carriage are connected to each other via an ink supply tube, and the ink is supplied to the ink jet recording head. The type facilitates an increase in volume of the ink tank, and is hence suitable for the purpose of using a relatively large amount of ink.
When recording is performed with the ink jet recording apparatus of such type, the ink supply tube for connecting the ink tank and the ink jet recording head mounted on the carriage is also routed in association with the reciprocation of the carriage on which the recording head is mounted, and hence the flexural rigidity of the ink supply tube is raised. As a result, a fatigue failure may occur when the hardness of the ink supply tube is high. Accordingly, the ink supply tube must have flexibility enough to resist the reciprocation. In particular, a reduction in size of an ink jet printer has been progressing in recent years, and higher flexibility has been requested of the ink supply tube at the time of the recording because reciprocation with a smaller flexing ratio is needed.
In addition, when moisture evaporates from the ink present in the ink supply tube to the outside of the ink supply tube, an increase in viscosity of the ink occurs, and the increase may cause serious problems such as a discharge anomaly and a reduction in print quality due to a change in composition of the ink. Accordingly, a high water vapor barrier characteristic is also requested of the ink supply tube.
Moreover, when an external gas such as air permeates into a tube material in the ink supply tube, the external gas dissolves in the ink in the ink supply tube, and hence a degree of deaeration reduces. Alternatively, a discharge anomaly or a reduction in print quality may be caused by the generation and growth of air bubbles in the ink. Accordingly, a high gas barrier characteristic is also requested of the ink supply tube. The gas barrier characteristic is extremely important particularly in an ink jet recording apparatus using a piezoelectric device because of the following reason. That is, a gas held in the ink supply tube serves as a cushion to prevent energy needed for ink discharge from being conveyed to an ink chamber, and the prevention may preclude the discharge.
Japanese Patent Application Laid-Open No. H09-300652 proposes an ink supply tube for ink jet recording of such a laminated structure that a material having ink resistance, small moisture permeability, and small rigidity is used in each of an inner layer contacting ink and an outer layer contacting external air, and a material having a low gas permeability is used in an intermediate layer. To be specific, a polyethylene is used as a material for each of the inner layer and the outer layer, and an ethylene-vinyl alcohol copolymer or a polyvinylidene chloride is used in the intermediate layer.
In addition, an approach involving using a thermoplastic elastomer having high flexibility in an ink supply tube for ink jet recording has also been investigated. For example, an olefin- or styrene-based elastomer is used as the thermoplastic elastomer. Japanese Patent Application Laid-open No. 2005-305878 proposes an ink supply tube for ink jet recording using a thermoplastic elastomer. To be specific, a styrene-isobutylene-styrene block copolymer (SIBS), a polyolefin, and a liquid polybutene are used, and the resultant ink supply tube for ink jet recording has an excellent gas barrier characteristic, an excellent water vapor barrier characteristic, and good flexibility.
However, such ethylene-vinyl alcohol copolymer or polyvinylidene chloride as described in Japanese Patent Application Laid-Open No. H09-300652 has high rigidity, though the copolymer or the polyvinylidene chloride has a low gas permeability. Accordingly, an ink supply tube using any such material that reciprocates upon recording has involved a problem concerning flexibility in terms of flex resistance. In addition, the case where a polyethylene is used in the outer layer has also involved a problem concerning a request for higher flexibility on the basis of the fact that reciprocation with a smaller flexing ratio has been requested in association with a recent reduction in size of a printer apparatus, though the case is suitable for a large printer application. In addition, the laminated structure ineluctably involves an increase in cost.
On the other hand, a tube using a thermoplastic elastomer is excellent in flexibility as compared to a non-elastomer member. Olefin-based thermoplastic elastomers have been widely used in the fields of automobile parts, industrial parts, and electrical and electronic engineering. Although the elastomers are excellent in water vapor barrier characteristic as well, an ink jet ink supply tube using any such elastomer has involved a problem concerning a gas barrier characteristic. Tubes each using a styrene-ethylene/butylene-styrene block copolymer (SEBS) as a polystyrene-based elastomer are excellent in gas barrier characteristic as compared to the olefin-based thermoplastic elastomers. Although the tubes have already been put into practical use in assorted applications, an additional improvement in gas barrier characteristic is requested of the tubes so that the tubes may be used for ink supply. Such tube using a styrene-isobutylene-styrene block copolymer (SIBS) as described in Japanese Patent Application Laid-open No. 2005-305878 involves a problem concerning moldability, though the tube is excellent in water vapor barrier characteristic and gas barrier characteristic. In addition, the use of the styrene-isobutylene-styrene block copolymer (SIBS) as a material involves a problem, i.e., an increase in cost.